We read the article “Prevalence of hidradenitis suppurativa in patients with axial spondyloarthritis” published in Reumatología Clínica journal with great interest.1 The study explored the prevalence of hidradenitis suppurativa (HS) in 265 axial spondyloarthritis (AxSpA) patients with the help of questionnaires and dermatologist confirmation. Of the 148 patients who completed the screening questionnaire, 2.7% had HS, greater than the general population rates.2 HS patients exhibited higher smoking rates, elevated disease activity, and shorter AxSpA duration. The results stress the importance of HS screening integration into AxSpA care to strengthen diagnosis and treatment. While their findings are significant and fill a significant gap in the literature by addressing important clinical correlations, several methodical limitations warrant discussion.

Firstly, although the cross-sectional study facilitates finding prevalence and association, it measures the exposure and the outcome but fails to establish a temporal relationship which prevents it from determining causality; whether the exposure led to the outcome or the outcome influenced the exposure.3

Similarly, the study does not mention whether a power analysis was conducted to calculate the sample size, which is crucial to detect the accurate prevalence of HS in AxSpA patients. Without it, the study risks a type II error which might result in the observed prevalence (2.7%) being statistically unreliable.4

Moreover, the study required patients to have experienced at least two HS flares in the past six months. However, the use of medications like GLP-1 receptor agonists and metformin in patients with coexisting diabetes and AxSpA reduces HS flare severity.5 This leads to the exclusion of a certain portion of patients, causing not only the underestimation of actual HS prevalence in AxSpA patients but also the overstating of associations with severe disease.

Selection bias may have influenced the results due to the exclusion of patients with cognitive impairment, language barriers, and certain comorbidities, overlooking the more vulnerable populations. Inequalities in healthcare access and disease severity amongst different groups also affect the prevalence estimates significantly.6 This limitation of the study can be addressed in future studies by adding a more diverse patient population that would enhance both the accuracy and applicability of the findings.

Additionally, underlying conditions such as thyroid disorders and calcium abnormalities, which can contribute to HS development, were not accounted for. These factors may have affected the accuracy of the study's prevalence estimates. We believe that the co-occurrence of such diseases should have been investigated a bit before carrying out the study to rule out if the development of HS was due to AxSpA or some other underlying disorder.7

Furthermore, we believe that even though the Hurley questionnaire used to estimate the severity of the disease is undoubtedly an inclusive and sensitive scale, it could have benefitted from a few modifications. Adding questions about the development of inflammatory nodules and abscesses formation before it progressed into a sinus may have resulted in a better assessment of HS severity and its progression.8 These amendments, in our opinion, could have enhanced the scope of the study and improved its quality.

A critical limitation of the study is the failure to adjust for confounding variables such as disease activity levels (e.g., BASDAI scores) and smoking status, both of which may differ between HS and non-HS groups. Addressing this limitation in future research would help ensure more accurate estimations of the true relationship between HS and AxSpA.

Despite these limitations, the study successfully highlights the prevalence of HS in AxSpA using a cross-sectional approach. However, its single-center design, selection bias, and lack of confounder adjustments restrict its applicability. Enhancing the Hurley questionnaire and implementing methodological refinements in future studies would strengthen the validity of these findings and their relevance to broader clinical practices.